Cellulose is a major substance that constitutes the cell walls of plants. Cellulose is a biomass material that is produced in a large quantity on the earth and is biodegradable in nature. Cellulose has been the subject of attention with the recent increasing interest in environmental protection.
Cellulosic materials are available in the form of fibers from plants in nature. Such cellulose fibers include, for example, cotton, hemp and pulp fibers. Cellulose fibers are used in various ways. For example, staple fibers, such as cotton and hemp fibers, are spun without further processing. Rayon and lyocell fibers are dissolved in solvents and wet spun to produce yarns. Cellulose derivatives, such as cellulose acetate, are dissolved in an organic solvent, such as methylene chloride or acetone, and are spun into yarns by dry spinning while evaporating the solvent.
Cellulose fibers have long been used due to their good wearability. The recent increasing demand for environmentally friendly materials has increased the use of cellulose fibers. Cellulose fibers are excellent in terms of sweat absorption because of their higher hydrophilicity than other fibers, thus being suitable for use in outdoor clothes, sports clothes, shirts and underclothes that are in direct contact with the skin.
However, since cellulose fibers are very ecologically friendly, they provide environments where various kinds of microbes grow, tend to produce unpleasant smells, such as smell of sweat, and generate static electricity. There is thus a need to develop an antimicrobial and deodorizing processing technique that imparts hygienic and safety functions to cellulose fibers.
Antimicrobial and deodorizing processing is not for the purpose of sterilization or treatment but is intended to inhibit the inhabitation and proliferation of bacteria and fungi on fibers. Antimicrobial and deodorizing processing should be safe in humans while persistently maintaining antimicrobial effects to some extent rather than high antimicrobial activity.
General organic antimicrobial materials are easier to process than inorganic antimicrobial materials and have no significant influence on the mechanical properties, transparency and color of fibers. Due to these advantages, organic antimicrobial materials have been predominantly used so far in fibers. Halamine, hydantoin, imidazolidinone, sulfadiazine and derivatives thereof are known as organic antimicrobial materials for use in cellulose fibers. These organic antimicrobial materials lack persistent antimicrobial effects and are particularly inferior in terms of heat resistance, which limits their use. Some organic antimicrobial materials cause problems such as skin irritation and lacrimation.
In comparison with organic antimicrobial materials, inorganic antimicrobial materials have good heat resistance and are highly stable without being volatilized and decomposed. Due to these advantages, inorganic antimicrobial materials can be used in a wide range of applications. Some metals, such as silver, copper and zinc, have strong antimicrobial activity and high safety and are currently known to be harmless to humans. However, since these metals tend escape from cellulose fibers, for example, during washing, their antimicrobial functions do not last long.
Many methods for imparting antimicrobial performance to fibers are known at present. Most of these methods are dependent on post processing of yarns or clothes. However, post processing is still unsatisfactory in terms of durability and fastness. For this reason, post processing is not actively applied to the clothing industry.
More specifically, post processing is limited in obtaining antimicrobial performance. For example, when a binder is added to fixedly attach antimicrobial particles to a cloth, only a limited amount of the binder is permitted, thus limiting the amount of the antimicrobial particles. Only a few cycles of washing causes the antimicrobial particles to escape from the cloth, and as a result, antimicrobial functions of the antimicrobial particles are lost. Many proposals have been made to solve the above problems. The present inventor has developed a skin-core short fiber having a bilayer consisting of a cellulose core layer and a metal skin layer (see Korean Patent Publication No. 2000-0059156). The short fiber is produced by coating a cellulose fiber with metal components.
High electrical conductivity of the metal skin layer ensures the ability of the short fiber to block electromagnetic waves and inhibit the generation of static electricity. Antimicrobial activity of the metal components makes the short fiber hygienically desirable.
However, the production of the skin-core short fiber involves complicated processing steps, including etching of the cellulose fiber, dipping in a reducing agent solution, dipping in a solution of a catalytic metal salt to uniformly deposit fine particles of the catalytic metal on the surface, pre-settling, and electroless plating. The metal constituting the skin layer is bound to the cellulose fiber constituting the core layer taking advantage of the affinity of the anionic polymer. Therefore, in response to changes in ambient environments, the binding force between the metal layer and the cellulose may gradually deteriorate, resulting in separation of the two layers.
Further, Korean Patent Registration No. 0876111 discloses a method for producing an antimicrobial fiber coated with silver nanoparticles. The method includes coating a mixed solution including silver ions and an aliphatic or aromatic amine compound on a fiber, such as cotton, containing alcohol functional groups. By the coating, the silver ions are sequentially adsorbed to the fiber surface through the oxygen atoms of the alcohol groups. The ions function as seeds for the deposition of the reduced silver.
Further, Korean Patent Registration No. 0396156 discloses a method for producing a functional fabric which includes mixing tourmaline, which is an inorganic material having good ability to generate anions, as a major factor with small amounts of other inorganic materials, mixing the tourmaline mixture with a pigment and an aid composition to prepare a padding solution, padding a fabric, such as cotton, with the padding solution, and sequentially pressing, drying, heat treating and tentering the padded fabric.
Further, Korean Patent Registration No. 0887768 discloses a method for producing a hydrous tissue having antibacterial and antifungal functions. The method includes impregnating a tissue fabric manufactured using a fiber (such as cotton) as a raw material with water containing metal nanoparticles and silver nanoparticles.
As described above, antimicrobial materials, such as silver, are mainly coated on the surface of fibers to provide antimicrobial performance to the fibers. However, the binding force between the antimicrobial materials and the fibers is not strong enough to prevent the antimicrobial particles from escaping from clothes, resulting in gradual deterioration of antimicrobial functions.